For a liquid-crystal display element to function, the direction of orientation of liquid-crystal molecules and the direction of polarization of the polarizer are closely related each other. In liquid-crystal display element technologies, LCDs using a TN (Twisted Nematic) type liquid-crystal has first been put into practical use, and then LCDs using a VA (vertical Alignment) type liquid-crystal, an IPS (Inplane Switching) type liquid-crystal etc., have been put into practical use. Although a technical explanation is omitted, in an LCD using such TN-type liquid-crystal panel, liquid-crystal molecules are provided between two upper and lower orientation films having respective rubbing directions on the inner surfaces of glass substrates of the liquid-crystal panel. This means that the liquid-crystal molecules are twisted by 90 degrees along the optical axis, so that when a voltage is applied, the liquid-crystal molecules are aligned in a direction perpendicular to the orientation of films. However, in the case where the LCD is designed to allow images as seen from right and left sides of a display screen as those view directly in front of the display screen, the direction of rubbing on the orientation film at the viewing-side must be 45 degrees (the rubbing direction of the other orientation film is 135 degrees). It is therefore necessary that polarizing sheets made from polarizing composite films to be laminated respectively on the front and back sides of the liquid-crystal panel must have polarizers respectively oriented in directions inclined by 45 degrees with respect to a lengthwise or widthwise direction of the display screen so as to conform to the rubbing directions.
Therefore, in a polarizing sheet for use in producing a liquid-crystal display element of a TN-type liquid-crystal panel, it is required that a optical film laminate is punched or cut into a rectangular-shaped sheet having a long side or a short side determined in accordance with the size of the TN liquid-crystal panel, in such a manner that the long or short side inclined by 45 degrees with respect to the orientation direction of the polarizer produced by stretching in the lengthwise or widthwise direction of a polarizer base film (i.e., with respect to the feed direction of the optical film laminate prior to the punching or cutting process). This is described in Japanese Laid-Open Patent Publication JP 2003-161935A (Patent Document 1) or Japanese Patent 3616866 B (Patent Document 2), for example. The optical film sheet of such rectangular shape has a width or a short side dimension which is smaller than the width of the optical film laminate. The rectangular-shaped sheets punched or cut from the optical film laminate may be collectively referred as “individualized sheets.”
In producing a liquid-crystal display element using such individualized sheets, each of the individualized sheets is punched or cut in advance with a separator adhered to an adhesive layer. The shaped individualized sheets are stored in a magazine in a liquid-crystal display element production process. The individualized sheets stored in the magazine are taken out and conveyed one-by-one by means of a suction conveyance unit to the lamination position with the liquid-crystal panel W. Before being laminated to the liquid-crystal panel W, the separator releasably laminated to a formed adhesive layer is peeled from respective ones of the individualized sheets, and each of the individualized sheets is laminated to the liquid-crystal panel W via as such exposed adhesive layer. As the individualized sheets are flexible, they tend to be bowed or warped on their edges, and thus it is a serious technical impediment in lamination with liquid-crystal panels. Thus, in producing a liquid-crystal display element using individualized sheets, it has been required to adopt individualized sheets having four trimmed sides and a certain level of stiffness for less deflection or bend and which can be conveyed and laminated easily, to facilitate peeling respective ones of separators one-by-one and an accurate and swift positioning and laminating respective ones of the individualized sheets with liquid-crystal panels. For this reason, the individualized sheets have been laminated with a protective film, for example, of 40 to 80 μm thick not only to one surface but also to both surfaces of a polarizer to have stiffness induced by a thickness. During the initial period in the history of the manufacturing process of the liquid-crystal display elements, the optical film sheet or a polarizing sheet comprised in such optical film sheet was generally known as “polarizing plate” which is still used as a common name.
In the manufacturing process of TN-type liquid-crystal display elements, it is impossible to obtain a finished liquid-crystal display element simply by sequentially laminating the sheets formed in the sequential punching or cutting process to respective ones of a plurality of liquid-crystal panels. This is because the sheet of the optical film laminate is cut from the web in such a manner that the sheet has a long or short side extending in a direction 45 degrees with respect to the orientation direction of the polarizer produced by stretching in a lengthwise or widthwise direction of the polarizer base film (i.e., with respect to the feed direction of the optical film laminate prior to the punching or cutting process), so that the sheet cannot be laminated sequentially to respective ones of the liquid-crystal panels with the orientation as it has been cut from the web. Therefore, to laminate the sheets to the liquid-crystal panel, each of the sheets need to be punched-out at an angled direction of 45 degrees from the continuous web of the optical film laminate having a width greater than a long side of the liquid-crystal panel with respect to the lengthwise direction of the optical film laminate, using, for example, a die, and fed to the lamination station where the polarizing sheets are laminated with the liquid-crystal panels, as seen in the Patent Document 1 or 2. Alternatively, the optical film laminate in use needs to be an elongated optical film punched or cut from the continuous web of the optical film laminate having a substantially large width in a direction 45 degrees inclined with respect to the lengthwise direction, or an elongated optical film formed with a plurality of formed sheets connected into a continuous film configuration. At any rate, the above methods do not provide any noticeable improvement over the method of using individualized sheets.
The Patent Document 3 is a Japanese Patent Publication No. 62-14810B which discloses, prior to the VA-type liquid-crystal and the IPS-type liquid-crystal are brought into practical use, an apparatus to produce a liquid-crystal panel element. According to the method disclosed by the Patent Document 3, a technique of continuously feeding out an optical film laminate is provided. The continuous optical film laminate comprises a polarizing composite film of substantial length (in the Patent Document 3, referred to as “elongated polarizing plate”) and a separator for protecting an adhesive layer provided on one side of the polarizing composite film and supplied in the form of a roll. The continuous optical film laminate is then unrolled from the roll of the film laminate and subjected to a process of “slitting only the polarizing plate 4 and the adhesive layer 5 while leaving the separator 6 uncut (hereinafter referred to as “half-cut”)” to thereby form polarizing sheets of desired dimensions. If it is found that anyone of the polarizing sheets contain a defect or defects, such defective or defect-containing polarizing sheet is removed from the process line in the course of the feeding. The polarizing film having no defect or defects are then peeled off the separator and sequentially laminated the liquid-crystal panels (in the Patent Document 3, referred to as “liquid-crystal cells”). It is interpreted that the method is proposed specifically for constituting small-size display screens for use with electronic calculators or the like. The apparatus is considered to be a type of labeler unit which produces an LCD using the TN-type liquid-crystal. There is taught to produce the optical film in the form of an elongated sheet, and for the purpose, an optical film laminate having substantially large width is provided and slit in a direction 45 degrees oblique to the lengthwise direction of the optical film laminate with a width corresponding to the width of the liquid-crystal pane. Alternatively, a film-like elongated optical film sheet may be formed by connecting a plurality of optical film sheets. Therefore, the method taught by the Patent Document 3 cannot be applied directly to a manufacturing process adapted to perform steps of continuously forming a plurality of polarizing sheets from an optical film laminate and laminating the respective sheets to respective ones of the liquid-crystal panels comprising VA-type or IPS-type liquid-crystal to produce liquid-crystal display elements.
The Patent Document 4 is a Japanese Patent Publication No. 55-120005B which discloses, prior to the VA-type liquid-crystal and the IPS-type liquid-crystal are brought into practical use, an apparatus to produce a liquid-crystal display element. The manufacturing method of an optical film laminate to be used in such apparatus is as follows. First, an adhesive layer is formed on a large-width polarizing composite film. A plurality of elongated polarizing composite film sheets having a required width are then provided by cutting the large-width polarizing composite film. These sheets are then applied to a separately prepared conveyance medium (i.e., a carrier film) which has preliminarily been subjected to a releasing treatment to produce an optical film laminate. Then, the optical film laminate is subject to a half-cut process in a transverse direction by means of two knives which are spaced apart by a required distance in the lengthwise direction, leaving the conveyance medium uncut. Thus the optical film laminate is sequentially cut into a plurality of sheets on the conveyance medium. Finally, the plurality of formed sheets are sequentially laminated to respective ones of the liquid-crystal panels being conveyed to manufacture the liquid-crystal display element. This apparatus is also based on the use of an elongated polarizing sheet which is cut in a direction 45 degrees oblique to the stretching direction of the polarizing composite film with a width corresponding to the width of the liquid-crystal panel. Therefore, the technology disclosed by the Patent Document 4 cannot be applied directly to a manufacturing apparatus adapted to VA-type or IPS-type liquid-crystal to produce liquid-crystal display elements.
Automation of manufacturing process for liquid-crystal display elements using individualized sheets is disclosed, for example, in the Japanese Patent Publication No. 2002-23151A (Patent Document 5). Flexible individualized sheets tend to be bowed or warped due to curves or distortion of its edge, and thus it is a serious technical impediment to accuracy and speed in registration and lamination with liquid-crystal panels. Thus, it will be understood that the individualized sheet is required to have a certain level of thickness and stiffness to facilitate registration and lamination with liquid-crystal panels typically in transportation under suction. For example, the disclosures in the Japanese Laid-Open Patent Publication No. 2004-144913A (Patent Document 6), Japanese Laid-Open Patent Publication No. 2005-298208A (Patent Document 7) or Japanese Laid-Open Patent Publication No. 2006-58411A (Patent Document 8) disclose measures for addressing such technical problems.
In contrast to TN-type liquid-crystal panels, the VA-type and IPS-type liquid-crystal panels are not designed to arrange liquid-crystal molecules in twisted orientations. Thus, in the case of the liquid-crystal display element using these types of liquid-crystal panels, there is no need to have the polarization axis of the polarizing sheet oriented at 45 degrees in view of viewing angle characteristics inherent to the orientation of the liquid-crystal. Each of these liquid-crystal display elements using these liquid-crystal panels is formed by applying the polarizing sheets to the opposite sides of the liquid-crystal display panel oriented with their polarization axes crossed at 90 degrees crossing angle. In the case of the VA-type and IPS-type liquid-crystal panels, with respect to the technical view point of symmetry of the viewing angle characteristics and visibility, maximum contrast can be obtained along the direction of the polarizing axis of the polarizing sheet, so that it is preferable that the sheets have polarizing axes oriented in parallel with the lengthwise or transverse direction of the liquid-crystal panel. Thus, it will be understood that these sheets to be applied to the liquid-crystal panel has a feature that the continuous web of the optical film laminate including a polarizing composite film which has been subjected to a lengthwise or transverse stretching can be continuously fed out from a roll and cut along transverse lines with respect to the lengthwise direction of the web of the optical film laminate to sequentially produce rectangular polarizing sheets including the polarizing sheets having the same width as the web of the optical film laminate width.
Because of the improved viewing angle characteristics, for liquid-crystal used in a display element for widescreen televisions, the VA-type liquid-crystal or the IPS-type liquid-crystal are more widely adopted than the TN type. In view of such trend in environments of technical developments, proposals to enhance the manufacturing efficiency using these types of liquid-crystal panels has been made such as the one described in Japanese Laid-Open Patent Publication No. 2004-361741A (Patent Document 9). This patent discloses steps of continuously feeding a continuous optical film laminate, cutting the continuous optical film laminate in conformity to the size of a liquid-crystal panel and sequentially laminating a plurality of optical film sheets which have been produced by the cutting step to respective ones of a plurality of the liquid-crystal panels.
However, the mainstream of manufacture of liquid-crystal display elements is still based on the manufacturing technology utilizing individualized sheets, due to the following technical problems. In manufacturing liquid-crystal display elements, a critical technical challenge is to detect any defect which may otherwise be retained in the display elements to be formed, and to prevent any defective product from being produced. Most of the product defects primarily arise from defects in the polarizing composite film contained in the continuous optical film laminate. However, it is not practical to provide an continuous optical film laminate after completely removing all defects contained in individual films which are to be laminated together to form the optical film laminate, because it is extremely difficult to produce a defect-free continuous optical film laminate under existing circumstances. To maintain quality of display elements, it is not permitted to use a polarizing composite film sheet having visible flaws or defects for a sheet for television display element even if such a flaw or defect is small. Given that the long side dimension of a polarizing sheet formed from the polarizing composite film is about 1 m, if a defective region cannot be preliminarily removed, 20 to 200 defective liquid-crystal display elements out of 1,000 products will be produced.
Proposals relating to preliminary inspection apparatus for a polarizing composite film have previously been made, as disclosed, for example, in Japanese Patent No. 3974400B (Patent Document 10), Japanese Laid-Open Patent Publications 2005-62165A (Patent Document 11) and 2007-64989A (Patent Document 12) for improving the production efficiency of manufacturing the individualized sheets. These proposals have disclosed technical means essential to improving yield in the manufacture of such individualized sheets.
Further, Japanese Laid-Open Patent Publications 2007-140046A (Patent Document 13) discloses a method comprising the steps of exposing a polarizing composite film having an adhesive layer by peeling a carrier film included in the continuous optical film laminate continuously fed out from a roll of continuous optical film laminate, detecting a defect or defects present in the polarizing composite film, punching only normal regions of the polarizing composite film in rectangular shape, appropriately avoiding defective regions, and conveying the punched normal polarizing sheets to the lamination position with the liquid-crystal panels by other conveying medium. It should however be noted that this process is not the one which makes it possible to feed the normal optical film sheets formed from a continuous optical film laminate to the lamination position with the liquid-crystal panel by means of the carrier film. This technique is a method for once laminating the cut individualized sheets to other conveying medium before conveying to the lamination position with the liquid-crystal panels, so this technique is not beyond the individualized sheet manufacturing system of liquid-crystal display element.
Japanese Laid-Open Patent Publications 2009-061498A (Patent Document 14) discloses a method for laminating the sheets of the optical film with the liquid-crystal panels and an apparatus therefor. This invention contains an innovative proposal allowing for shifting from a liquid-crystal display element manufacturing system designed to carry a plurality of preliminary formed individualized sheets in the manufacturing process of the liquid-crystal display element, and laminate the individualized sheets one by one to respective ones of a plurality of liquid-crystal panels, to a continuous manufacturing system for liquid-crystal display element designed to continuously form a plurality of optical film sheets and directly laminate the formed sheets to respective ones of a plurality of liquid-crystal panels.
However, the method and system disclosed cause not only substantial complexity in the entire system for laminating but also an increase in the number of steps and difficulty in control for each step, and thus causes reduction in the manufacturing speed.
The present invention has been made based on the aforementioned prior proposals and through intensive researches and considerations for enabling a sequential manufacturing of liquid-crystal display elements and significantly enhancing product accuracy and manufacturing speed, and drastically improving manufacturing yield, in the manufacture of liquid-crystal display elements.
The prior art documents referred to in the above descriptions are listed below.                Patent Document 1: Japanese Laid-Open Patent Publication 2003-161935A        Patent Document 2: Japanese Patent No. 3616866B        Patent Document 3: Japanese Patent Publication 62-14810B        Patent Document 4: Japanese Laid-Open Patent Publication 55-120005A        Patent Document 5: Japanese Laid-Open Patent Publication 2002-23151A        Patent Document 6: Japanese Laid-Open Patent Publication 2004-144913A        Patent Document 7: Japanese Laid-Open Patent Publication 2005-298208A        Patent Document 8: Japanese Laid-Open Patent Publication 2006-58411A        Patent Document 9: Japanese Laid-Open Patent Publication 2004-361741A        Patent Document 10: Japanese Patent No. 3974400B        Patent Document 11: Japanese Laid-Open Patent Publication 2005-62165A        Patent Document 12: Japanese Laid-Open Patent Publication 2007-64989A        Patent Document 13: Japanese Laid-Open Patent Publication 2007-140046A        Patent Document 14: Japanese Laid-Open Patent Publication 2009-061498A        